Shatterproof plastic



oci. 23, 1945.

B. ANDERsEN r-:rAL v 2,387,227 SHATTERPROF IPL'STICS Filed March 2o, 1.942

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l5- ANDEREN Patented Oct. 19u45 UNITED i 'STATES 2,387,227 snsr'rsarnoor PLASTIC Biorn Anderson, Mopiowooa, and iii-nest` Orme.

Schweizer, yEast N. J., assignors to Celanese Corporation oi' America, :Loot-poration oi' Delawarev f annotation Moron 2o, 1942, sei-iol No. 435,490

s cioimnf (ci. 154-2) This invention relates to the preparation of shatt'erproof glass substitutes, and relates more 'particularly to the preparation fof plastic vcomposites which are resistant to the shattering effects of bullet impact even at sub-zero temperl atures.

An important object of this invention is the provision of windows and windshieids in oookpits.' gun turrets and other compartments for aircraft -built to y in the stratosphere where l they are subjected to Iowtemperatures.

Another object of this invention is to provide plastic compositesv having high clarity. good weathering characteristics. vand that are shatterproof particularly at low temperatures. l

-Aiurther object oi this invention is to provide a shatterproof plastic composite capable 'oi' being hot-formed` into three-dimensional shapes for aeroplane nose sections; turrets and similar parts.

Other objects oi' the invention will appear .20

froml the following detailed description and `In the drawing there are shown several modiilcations of our invention, the reference characters referring to the same or similar elements in the respective views.

Fig. 1 is s. cross-section of onefmcdication of our invention,

Fig. 3 isa plan view, on a reduced scale, of

the 'modiiication shown in Fig. 1, f 3o Fig. 3 is a cross-sectional view of the modi# I iication shown in Fig. 1 showing in detail the position of the shatter controlling wire in a compositemolded to a three-dimensional shape.

Figs. 4. 5 and 6 are cross-sectional views of 35 other modifications oi' our invention.

A great need has developed for transparent plastic sheet material suitable for use iin warA and commercialaircraft as window panes and windshields in cockpits. gun turretsand other 40 compartments. Bombersk often operate at an altitude lof 35,000 feet, which is weuwithin the stratosphere.' where the temperature remains constant' at about 70 C. As is well known,

the cabins of such aircraft are under suitable pressure. Moreover, such aircraft may be based in the tropics where theinterior of the cabins may attain a temperature as high as F. ConsequentLv, materials intended for this use must withstand such temperatures without loss. of 5 shape. Furthermore, the materials when used i in war aircraft must be shatter-proof such that the impact of a bullet would not shatter a pane allowing a quick drop in pressure in cabins which -x are under pressure.

'remembered that complete resistanoe to bullet penetration is not sought. yWhat is desired, and

is solved vby the present invention, is freedom from Y shattering under the impact of a bullet, restrlct- Y ing the size of the hole and the radiating cracks to, an area only slightly larger than the bullet. II a bullet were to penetrate and completely shat-` ter a section of a window, it would be impossible to maintain the desired hishzpressure in the cabin and the occupants would be in danger.' The relatively small holes, such as those vmade by machine gun bullets in a pane of the plastic composite of the present invention, can easily andquickly be patched by placing cellulosic adhesive tape, or cementing plastic discs over them, without substantial loss of pressure.

In accordance with our invention, we produce a composite plastic having an inter-layer with a metal wire insert floating therein, which irltei-layer is relatively soit at its forming or shaping temperature. In one of the most simple n v iormsthe composite plastic material, producedin accordance with this invention, 'will consist of three layers, an inner soft plastic -layervv having a wire. mesh iloating therein bounded or laminated on each side to a more rigid, harder and more scratch-resistant outer plastic layer.l By

the term "hosting," as herein used. is meant that atthe forming temperature where the composite sheets are drawn or bent a moldwith heat and pressure to three vdimensional shapes. the plastic layer containing the wire is sufiiciently iiuid to allow some movement and deforming of the wire without cutting their-yer and to equalize any stress produced by the movement of the wire such that the clarity ci the resulting-product is not impaired by distortions, displacements. light refractions and strains set uip in the plastic. Many inodiiications` may be produced with the above basic principle in mind. as will be clear from av description ofthe invention with reference to the drawing. 'L

' In Figs. 1, 2 andi) there is .shown one modication of our invention' comprising aiplastic layer A having an open wire mesh W oatlng therein with harder scratch-resistant layers B' and C laminated thereto with an anti-fogging layer D coated on orlaminated to the layer B,

or, as shown in Fig.-5, to both layers B and C. l

and, as shown in'Fig. 6, to the layers B and. A. therebeing no layer C in this particular modliication. The layer A may comprise highly plas-l f f ticized cellulose derivative sheets, having a base of cellulose acetate, cellulose acetate-propionate.

mltmsrespect, it must be cellulose actatebutyrate, cellulose -nitrate' or other cellulose ester or cellulose ether, such as ethyl cellulose, benzyl cellulose, etc., some of which are described with reference to laminated glass in Walsh U. S.' Patent No. 1,936,044. VAny suitable plasticizer may be employed in the preperation of the various cellulose derivative layers,

the amount and type depending upon the composition 'of the layer in the composite. Among the cellulose derivative 4plasticizers which have been found suitable are dimethoxy ethyl phthalate, dimethyl phthalate, diethyl phthalate, triacetin, dibutyl tartrate, methylv phthalyl ethyl glycollate, para ethyl toluene sulphonamide, etc. Mixtures of these plasticzers and fire retardants, such as triphenyl phosphate, may also be employed. For the inner soft layer, water-soluble plasticizers may be employed, particularly" those imparting flexibility at low temperatures such as, for example, isobutylene glycol and polyglycol derivatives, suchas trior tetraethylene polyglycol esters and ethers. The outer hard layers of the composite are preferably made with Where. cellulose acetate-butyrate is employed a particularly eiiective plasticizer is butyl phthalyl *butyl glycollate, while the preferred plasticizers r for ethyl cellulose are a. mixture of ortho and polymerized vinyl acetate, co-polymers of vinyl acetate and vinyl chloride, polymerized vinyli dene chloride, polymerized methyl and/or ethyl acrylate, polymerized methyl methacrylate, polymerized styrol and polyvinyl acetalv sheets.

.These products appear in the market 'under various trade names, respectivelyl such asv Gelva, Vinylite, Saran, Plexigum, Lucite, Lustron and Butacite. The preferred plasticlzers for use with synthetic resins are methyl phthalyl `ethyl glycollate and dibutyl phthalate and tricresyl phosphate, although any other suitable plasticizer may be used.

Our invention also contemplates the use of combinations of cellulose 'derivatives and synthetic resins. Thus, layers B and C may be plasticized cellulose acetate, while the inner layer may be a soft plasticized polyvinyl acetal resin, i. e. Butacite. These heterogeneousr layers are united to each other by the use of suitablymutually actingsolvents as cementing aids between the various layers.-

In layer A is embedded an open wire mesh W. This wire mesh is not intended to substantially strengthen the composite but is provided to limit the shattering effect or cracks l that radiate from a bullet hole 2. The wire is preferably of ne gauge, say about 16 gauge, and is woven in a mesh of various shapes. i. e. square, hexagonal, etc., and of such dimension that there is little interference with optical clarity. 'I'he wire is preferably a high tensile strength steel. or suitable alloy, etc., and is preferably provided with crimped portions 3. 'I'he crimped portions -g Water-proof or weather resistant compositions.

for stratosphere plane' gun turrets, the totaly wire as a fabric to be stretched. As shown in Fig. 3, the wire as a fabric moves, relative to layer A, on bending and it no longer need be in the center as shown in Fig. 1. It is this move-V ment of the wire in layer A during the molding that gives rise to the term iloating The softer layer A should be sufficiently tough and adhesive to hold the broken fragments of the outer layers together when broken, and should be soft and flowable at an elevated temperature, such at 325 F., or within the range employed in shaping, molding or bending of the completed composite. Such molding temperatures will depend upon the composite layers and will usually be above 200 F., say about 325 F., for cellulose acetate layers. The wire mesh may be embedded in the layer as it is formed by casting or extruding methods or two preformed or "cut sheets may be. laminated together with the wire interposed therebetween. The wire may be precoated with a, soft plastic composition. Furthermore, a wire fabric may be placed upon a soft preformed sheet and'a layer of plastic flowed, brushed or sprayed over the Wire fabric. The thickness of the layer A will depend upon the gauge of wire employed, the radius of the bend or bends and, as this layer is usually the pliable, adhesive layer which prevents the flying of splinters, its inherent strength. Obviously,

A that the optical clarity of same is at its 0pthe layers shown in allow amovement of the wire in molding operations without its snapping, that is, it allows the in` any desired manner.

timum. In this respect it may be stated that the drawing are not to be considered limitations.

The layer B may be of the same chemical mai teria! as the layer A and have the same general properties, or itmay be a. layer of harder and/or .'40 tougher material. The thickness of layer B may vary from, say, .050" to .300", vor more, depending on the particular application., Furthermore, the layer B may be in itself built up of two or more layers each of increasing hardness and/or toughness or hard and tough layers interposed Thus, the outer surface of layer B may be a. layer such as D in the drawing, which layer may comprise a cast nlm of 0.01' or less in thickness and relatively hard in character better to withstand abrasions and also to overcome objectionable "knife lines" that often reappear in "cut sheets during the molding operation. The layer C` may be of the same composition and thickness as layer B or of an entirely dierent plastic material and/or properties. Layers B and C need not be of the same thickness. As shown in Fig. 6, it isnot necessary to have both a layer B and a layer C but either may be dispensed with, or both may be combined into onelayer on one side of the layer A. The

composite may be built up of two or more layers,

say, 3, 4, 5, 6 and '7 layers. V.

In some instances it is desirable to provide an anti-fogging layer D to one (Fig. 1) or both (Fig. 5) sides of the composite. This may be a thin filnr of cellulose acetate treated with, a saponifying agent either before or after vlamination to the composite or it may be a coating of f any material suitable for such purpose. D may point of impact. 'riie composite nsture of the finished sheet prevents flying pieces in much the same manner as laminated glass and the embedded wire fabric tends to limit the-run or length of the cracks to a single or a few. wire meshes'.

The oating of the wire in the layer asomar A, et the molding temperature. permits bending and molding without producing stresses or displacements that interfere with clarity.

If desired, one or more layers of thev composite mayl contain dyes and/or ultra-violet' light absorbers. Incertain instances it may be made A 'sheet of plastik-.material comprising a soft plastlcized polyvinyl acetal resin (Butacite) of a thickness of 0.06" and having an open mesh wire fabric lembedded therein is laminated between two Lucite (polymerized methyl methacrylate resin) sheets each having a thickness of 0.10". v

y Example VI i 'A sheet or piestic material .ooim'irisin'g a-sort plasticized polyvinyl acetal resin (Butacite) of a opaque or translucent, "as distinguished from optically clear',` by pigments' and fillers.l

The following examples illustrate the invention, but are not to be considered in any way:

Example I A sheet of soft plastic material having a thickness of 0.10" of the following composition:

. y Parts by weight Cellulose acetate e 100 Dimethoxy ethyl phthalate 80 `and having an open mesh wire fabric embedded therein is laminated between two harder sheets 0.05" in thickness having the following composition:

Parts by weight ACellulose acetates... -.1100 Dimethoxy ethyl phthalate 30 :sample 1I A siieet or piestic materies having e thickness of.0.l5" of the following composition:

' 'Y Partsbyweight. Ethyl cellulose 100 Methyl phthalyl ethyl glycollate 35 Suitable stabiliser QS.

Ewample III Y I Parts br weight Polymerized vinyl acetate 9,00 'Methyl phthalyl ethyl glycollate ;-f'l

and having an open mesh wire fabric embedded as limiting it thickness o! 0.06" and having Aan. open mesh wire fabric embedded therein is laminated between two polystyrol sheets each having a thickness of 0.10". i

The compositeformed in accordance with the y foregoing examples may beshaped and exposed to temperatures as high as 140 F. without lossl of shape. These compodtes all show high resistance-to shattering on bullet impact, the bullet passing through the same without shattering or breaking the composite and with substantially no cracmng of the layer on the exit side, even at temperatures in the vicinity of C. which are experienced in the stratosphere. Where any cracking does take place cracks extend to the wire mesh without soins beyond the same.

-The hardness of the layers"of plastic materials employed in accordance with this invention l may be determined and reported in several ways;

' The indentation hardness of plastics is generally measured by the vBrinell and Rockwell methods which are well known in the plastic industry. In these two methods a hardened steel ball is pressed into a smooth surface of the material being test- I ed. In the Brlnell method the spherical area of the resulting indentation is measured by calculation from this value and the applied load.y In' the Rockwell system the depth of the indentation is measured by means of an arbitrary scale,

which. scale dillers for each type of material The Rockwell scale'for plastics is desigv so A sheet of plastic material having a thickness l of 0.06 of the following composition: I'

'therein is laminated between twosiieets diev and 0.20", respectively, 4iii thickness having the following composition:

, l i Pei-ts by weight Polymerized vinyl acetate 100 Methyl phthalyl ethyl glycollate 25 l plasticized polyvinyl acetal resin (B'utacite) of a. thickness of 0.06," and having an open mesh wire abric embedded therein is laminatedto .a 'sheet .1o-nin thickness having the vfollowing composinated by the letter M. see Government Printing Oiilcs Publication L-P-406 'of December 9,

1942 bearing the title "B ederal Standard Stock Catalog wherein in Section IV (Part 5) is elven methods of testing organic plastics. The hardness may also be reported in terms of Vickers numbers and Shore's scleroscope numbers, pare ticulerly where the sheet is too soft to measure under conditions of the Brinell and Rockwell tests. The Bhore's scleroscope number is the rebound, measured onan arbitrary scale of 140, of a-hamrner with a diamond striklngpolnt falling freely from a height of approximately iii," (Model D instrument). 'mae Vicker's test is made with a5 kilogram load applied on a diamond pyramid for 'l seconds.

" Sheets of the following hardness have been -found suitable in forming the composites of the instant invention, although it is to be understood a that sheets o! other hardnesses may be employed.:

05 A neet or piseticmsterisi comprising e soit Cellulose acetate soft sheets having a Vlckers number slightly higherthan 3; cellulose acetate hard sheets having -a- Brinell hardness (2.5 mm.

ball, 10 kt. 10nd)v of 6"-15, or a Rockwell hardness of M25 to M55: Butacite sheets having a Vickers number of about 3 and a Shore scleroscope num- 'ber of about 45; Lucite sheets having a Brinell f hardness (2.5mm.- ball, 25 kg. load) of 18-20, a

Rockwell hardness crust-M105, s shore scleroscope number of'l and a Vickers number of 18.4; and Dblyltyrol sheets having lBx'lncll hard- ,nels f2.6 mm. bail, 25 kg. load) oi- '3o-30, a Recke' well hardness of M55 to M90, a Shore scleroscope number of 65 and a Vickers number of 20.

v posite material comprising a layer of relatively soft plastic material, having embedded `therein an open mesh wire fabric the wires of which have crimps along the length thereof, and a layer of harder plastic material at a temperature which causes said relatively soft plastic material to soften so as to permit the wire'fabric to iioat during the molding operation, whereby the molding into a three-dimensional shape is eiected without snapping the wires and without producing stresses in said composite material. y

2. Process for the preparation of shaped plastic composite material having high resistanceY to shattering from bullet impact, which comprises molding into a three-dimensional shape a com-- posite material comprising a layer of relatively soft plasticized cellulose acetate material, having 30 embedded therein an open mesh wire fabric the wires of which have crimps along the length thereof, and a layer of harder plasticized cellulose acetate material at a temperature which causes said relatively soft plasticized cellulose acetate material to soften so. as to permit the wire i'abric to iioat during the molding operation, whereby the` molding into a three-dimensional shape is effected without snapping the wires and without producing stresses in said composite material.

3. Process for the preparation of shaped plastic composite material having high resistance to shattering from bullet impact, which comprises molding into a three-dimensional shape a composite material comprising a layer of relatively soft synthetic resin material, having embedded therein an open mesh wire fabric the wires of which have crimps along the length thereof, and a layer oi' harder synthetic resin material at a temperature which causes said relatively soft synthetic resin material to soften so as to permit the wire fabric to iioat during the molding operation, whereby the molding into a three-dimensional shape is effected without snapping the wires and without producing stresses in said composite material.

BJORN ANDERSEN. ERNEST SCHWEIZER. 

